Oak Pinhole Borer – from rarity to pest

In Britain, the Oak Pinhole Borer (Platypus cylindrus) used to be regarded as a rare beetle of mainly ‘veteran’ oak trees, but following the 1987 gales their numbers increased rapidly in the south and south-east in fallen hardwood timber.

Oak Pinhole Borer breeds in cut and windblown trees, and standing dead and dying trees; it occurs primarily in oak but also in other important timber species. It does not kill trees or significantly weaken their timber but it does spoil the wood’s appearance and so reduces its value for veneers or high-quality structural timber.

The small brown/black adult beetles are 6 to 8 mm long and have a life cycle from egg to adult of two years. The larvae feed on ambrosia fungi that grow on the walls of their tunnels after being brought in as fungal spores carried on the adult beetles. Sporadic emergence of mature beetles has been reported throughout the year but most adults emerge between June and September. Cut logs are most vulnerable to attack between mid-July and mid-September, the period when the beetles are at their most active.

Chemical treatment can stop the beetles entering uninfected logs, but once beetles have tunnelled into a log they cannot be controlled successfully with insecticide. It is better and more environmentally friendly to protect logs by taking account of the biology of the beetle when harvesting.